Three U.S. House Democrats on Monday asked the head of the Federal Aviation Administration (FAA) to provide more details of the agency’s oversight of Boeing’s (BA.N) 737 MAX and questioned whether the planemaker had been held fully accountable. The best-selling, single-aisle airplane, which was grounded for 20 months after two crashes killed 346 people in the space of five months, returned to service in late 2020. The lawmakers, including House Transportation and Infrastructure chairman Peter DeFazio, asked FAA Administrator Steve Dickson in a letter Monday what the agency had done, if anything to hold Boeing employees responsible for various transgressions. It asks for a response by Dec. 13. The letter said these included Boeing’s apparent violation of its approved 737 MAX type design, as well as evidence of an internal plan to downplay the significance of a key safety system called MCAS tied to both fatal crashes. An FAA spokeswoman …